In a laser processing machine, the distance of propagation from the outlet of a laser oscillator to a condensing lens is a factor which has a great influence on the workability. Although a propagation path can be fixed in a laser processing machine of a moving-workpiece type, this arrangement is unfit for high-speed processing on account of the high inertia of moving workpieces.
In a laser processing machine of a moving-processing-head type, on the other hand, the length of an optical propagation path which connects a laser oscillator and condensing means varies depending on the moved position of a processing head. In order to maintain an optical path length fit for the laser radiation characteristic, therefore, it is necessary to extend or contract the optical path length of a laser beam in some region on the propagation path, thereby continually keeping the length of the propagation path from the laser oscillator to the condensing means at an optimum value.
As a measure to attain this, a laser processing machine arranged in the following manner has already been proposed as Published Examined Japanese Patent Application No. 1-55076. In this machine, pairs of reflectors for refracting the optical path of the laser beam at 90.degree. at a time so that the laser beam is emitted parallel to the incident beam are arranged for a specific drive axis of the processing head or separately for individual drive axes, and, according to the movement of each axis, each pair of reflectors are jointly moved for half the distance covered by each axis in the direction of the optical axis, taking advantage of the principle of running blocks, ball screw pitch ratio, or reduction gear ratio. By doing this, the length of the propagation path from the laser oscillator to the condensing means is kept constant.
In this laser processing machine disclosed in Published Examined Japanese Patent Application No. 1-55076, however, drive means for the individual axes for driving the processing head and the reflectors for the individual axes are directly linked by means of a mechanical interlocking mechanism, such as running blocks, ball screws, gears, etc., or otherwise, drive means for the reflectors are arranged separately from the drive means for the individual axes. In either case, the rotating speed of the drive means for the reflectors can adaptively be controlled only to the extent of half the moving speed of a specific drive axis for the reflectors.
Thus, if the aforementioned invention of Published Examined Japanese Patent Application No. 1-55076 is applied to a laser processing machine of a multi-axis control type in which the processing head is moved in the directions of the various axes, the length of the propagation path of the laser beam must be adjusted for each axis, in order to keep the propagation path length constant, so that an extra pair of reflectors must be arranged for each axis, thereby causing problems such as the increase in the complexity of construction and demand for high-accuracy guide members for the moving reflectors, which entail higher manufacturing cost, as well as the problem of attenuation and radiation of the laser beam.
Furthermore, in the laser processing machine disclosed in Published Examined Japanese Patent Application No. 1-55076, the pairs of reflectors, which constitute optical path length adjusting means, move directly in association with the movement of the processing head through the medium of the mechanical interlocking mechanism, such as the running blocks, ball screws, or gears, so that the length of the propagation path from the laser oscillator to the condensing means is fixed. Thus, the length of the propagation path itself cannot be adjusted in accordance with processing conditions, such as the kind of material and thickness of workpieces, and in some cases, it becomes impossible even to set an optimum propagation path length for processing.